Effects of interfaces and current spreading on the thermal transport of micro-LEDs for kA-per-square-cm current injection levels.

The three-dimensional thermal characteristics of micro-light-emitting diodes (μLEDs) on GaN and sapphire substrates were studied with forward-voltage methods, thermal transient measurements, and infrared thermal imaging. The μLEDs on the GaN substrate showed an approximately 10 °C lower junction temperature and smaller amplitude of the factors than those on the sapphire substrate under the current injection level of 4 kA cm. The thermal transient measurement showed that the spreading thermal resistances of the mesa, the GaN epilayer, and the interface of the GaN/substrate were reduced significantly for μLEDs on the GaN substrate because of the high-quality GaN crystal and the homogeneous interfaces. The infrared thermal images showed lower total average junction temperatures and more uniform temperature distributions for the μLEDs on the GaN substrate, which were also simulated with APSYS software. The thermal transport mechanisms are discussed for the lateral and vertical directions in the μLEDs.